The market is requiring that designers can understand programming concepts and programmers can understand designing concepts.
In an ideal world, everybody designing for the web medium would also be a front-end developer. The reasons for this are simple – design is development. To truly get the most out of your design skills, you need to be at one with the environment in which you design. Interestingly, many designers from an offline/print background get tasked with designing for the web; cue extraneous design concepts that attempt to detail interactivity and demonstrate web pages at different screen sizes.